This invention, in one of its aspects, relates to a process for determining the quantity of hydrogen chloride (HCl) in the atmosphere. In another of its aspects the invention relates to improved apparatus for such determinations. In still another of its embodiments the invention provides a rapid process which, on a real-time basis, that is, without a reaction-time delay, can be relied upon by personnal with a need to enter an area after an HCl-generating event.
There is concern within the military community over the potential health effects from combustion products resulting from the firing of various weapons systems. Of particular interest are the relatively high concentrations of HCl produced by combustion of rocket propellants used in U.S. Army weapons systems such as the STINGER and Multiple Launch Rocket System (MLRS). Some propellants used for rocket fuels are perchlorate-based and form HCl as one of their combustion products. Systems, which use perchlorate-based propellants, create potentially hazardous field exposures for operators. Personnel associated with rocket firings may be exposed to short-term decrements in performance. Monitoring methods used by various agencies and contractors were evaluated in test firings of the STINGER and CHAPARREL rockets. Noticeable limitations in monitoring capability observed during these field testings included the lack of field calibration and the lack of replicate sampling from identical sample points. The primary methods utilized for HCl monitoring were the batch-type midget impinger and the continuous-type Geomet.TM. HCl monitor. The midget impinger traps all forms of HCl, but it does not provide real-time data. The Geomet.TM. HCl monitor measures HCl on a real-time basis, but it has not been established that the Geomet.TM. method detects all forms of HCl. HCl can be present as a gas, as an aerosol, or as HC1 adsorbed on particulate matter.
When the STINGER is fired operators remain in the launch area during the launch. In the case of other launches, there is usually a need to re-enter a launch area as soon as possible after a firing. Such personnel need to know how safe such areas are. In order to assess potential health hazards, all forms of atmospheric HCl must be monitored on a real-time basis. There is an obvious and urgent need to develop an atmospheric monitor that detects all forms of HCl on a real-time basis in order to accurately evaluate potential health hazards. With such information, recommendations can be made relative to personnel protection and weapons design.
In 1985, at the JANNAF Safety & Environmental Protection Subcommittee Proceedings I presented a method for determining hydrogen chloride in the atmosphere on a near real-time basis. The presentation was published by the Chemical Propulsion Information Agency in CPIA Publication 436, November, 1985 herein incorporated by reference. The method described incorporated the principles of both midget impinger techniques and flow injection analysis. The impinger techniques were designed to extract HCl gas, aerosol forms of HCl, and HCl adsorbed on particulate matter into a trapping solution. Flow injection analysis allowed for continuous sampling and replenishing of the impinger reservoir of trapping solution. By using small diameter tubing and reducing quiescent zones, or dead volumes, throughout the system, it was possible to approach, although not as closely as desired, real-time monitoring of total HCl. A response time, the time for obtaining results, of 5 seconds, although not attained, was desirable since such a period would coincide with the frequency of normal breathing.
In my 1985 process air was drawn in through a miniature impinger, at approximately 1,000 mL/min. Trapping solution (water or a buffering solution) was pumped into the impinger at its front end. By the time this mixture reached the end of the impinger, the trapping solution had extracted about 95 percent of the total concentration of HCl in the atmosphere sample. The air/liquid mixture was separated and air was drawn off, while the trapping solution was withdrawn for testing. In testing, the trapping solution, and chloride reagent containing Hg(SCN).sub.2 and Fe(NO.sub.3).sub.3, were mixed, and the mixture was passed through a 37.degree. C. temperature bath and into a flow cell. Therein the absorbance was measured at 480 nm with a colorimeter. The response was monitored by a strip chart recorder. There was a delay of about 15 seconds from the time HCl entered the miniature impinger until a deflection was noted on the strip chart recorder. Another period of roughly 13 to 15 seconds was required for a monitor to reach 90 percent of total response. The response time thus was longer than the desired 5 seconds, and while the monitor responded to all forms of atmospheric HCl, the HCl response was from about 1 to 100 ppm. It was reproducible, but non-linear. There is, then, a need for a monitor meeting such criteria as a response time of 5 seconds or less, and a linear, more accurate HCl response. For this reason the 1985 monitor was not considered finally developed. By this invention a fully developed process, and apparatus for carrying out the process, is provided meeting those criteria.